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Write the steps involved in the free radical mechanism in polymerisation of ethylene.OR Explain the free radical mechanism for the polymerisation of ethylene. |
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Answer» Solution :Polymerisation of ETHYLENE is carried out at high temperature and at high pressure in presence of small amount of benzoyl peroxide as intiator. Formation of free radicals : The first step involves clevage of benzoyl peroxide to form two carboxy radicals . These carboxy radicals immediately undergo decarboxylation to give PHENYL intiator free radicals.  (2) Chain initiating step : The phenyl radical thus formed adds to ethylene to form a new larger free radical.  (3) Chain propagation step : The larger free radical formed in the chain initiating step reacts with another molecule of ethene to form another big size free radicals and chain GROWS . This is called chain propagation step. `C_(6)H_(5) - CH_(2) - overset(*)CH_(2) + CH_(2) to underset("bigger free radical")(C_(6)H_(5) - CH_(2) - CH_(2) - CH_(2) - overset(*)CH_(2))` The chain reaction continues till thousands of ethylene molecules are added. (4) Chain TERMINATING step : The continuous chain reaction can be TERMINATED by the combination of free radicals to form polyethene. `2 C_6 H_5 ( CH_2 -CH_2)_n - CH_2 - overset(*)CH_2 to underset("poyethene (polymer)") (C_6H_5 ( CH_2 - CH_2)_n )- CH_2 - CH_2-CH_2 -CH_2 ( CH_2-CH_2)_n - C_6 H_5 ` |
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